In manufacturing microelectronic devices, structures are formed in layers using lithographic processes. In such processes, resist patterns in a mask are projected onto a resist material deposited on, for example, a semiconductor wafer. Extreme ultraviolet (“EUV”) lithography uses short wavelength radiation (e.g., about 13.5 nm) to form smaller microelectronic devices than produced by earlier methods. Due to the short wavelength employed in EUV lithography, EUV masks typically comprise a substrate, a reflective multilayer mirror (i.e., a Bragg reflector) disposed on the substrate, and a patterned masking layer disposed on the multilayer mirror. However, defects may arise during the manufacturing of EUV masks that cause errors in the resist patterns.
Defects within or beneath the multilayer mirror of a EUV mask are called multilayer defects. Multilayer defects may be local deformations of the multilayer mirror due to bumps or pits on the substrate surface that result from, for example, particles, scratches, or other localized variations in thickness. Multilayer defects may cause a variation of the phase and/or amplitude of the ultraviolet radiation projected by the multilayer mirror due to interference. These variations, in turn, may cause defects in the resist materials used to pattern semiconductor wafers.
Most, if not all, EUV masks contain some sort of multilayer defect. Because a particular EUV mask is repeatedly used to manufacture numerous devices, any multilayer defect occurring in the EUV mask impacts all the devices subsequently manufactured. As such, error correction can be attempted to minimize the effects of the multilayer defects. Poor error correction methods insufficiently minimize the multilayer defects, which reduces yield and quality of microelectronic devices manufactured using the EUV mask.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.